Multi-group multi-wavelength laser matrix

ABSTRACT

A laser system capable of producing multiple groups of output wavelengths is disclosed. In one embodiment, an optical fiber bundle ( 20 ) doped with erbium (Er) or erbium/ytterbium (Er/Yb) is perpendicularly attached to an optical device ( 10 ), which serves as a guided-mode resonance feddback mirror, to form a fiber laser matrix. The optical device contains a substrate layer ( 11 ), a waveguide layer ( 13 ), and a grating layer ( 14 ), with non-uniform device parameters. The wavelength of the resonant light and its corresponding laser light of an individual optical fiber depends upon the parameters in the location on the optical device where the fiber is attached. In another embodiment, a plurality of active waveguides in a body are attached to an optical device to form a diode-pumped crystal laser matrix with multi-group output wavelengths.

FIELD OF THE INVENTION

The present Invention relates generally to optical networks, and moreparticularly to multi-wavelength laser technology.

BACKGROUND OF THE INVENTION

Multi-wavelength lasers (MWLs) are useful in providing multiple-channellight sources for optical networks, especially for dense wavelengthdivision multiplexing (DWDM) systems. The desirable features of MWLsused for DWDM systems include compact design, high stability in theoutput wavelengths and wavelength spacing, reasonable output power, widewavelength range and narrow linewidth for a large channel capacity,convenience of modulating individual wavelength at a high rate, andeasiness of manufacture. In addition, the wavelength-locking mechanismsof MWLs should be as simple as possible. No existing MWL provides allthose features largely because of the limitations in current lasertechnologies.

A number of MWL technologies have been investigated, and they can begenerally classified into two types: MWL array and shared-gain MWLs. AnMWL array consists of a row of single-wavelength lasers such asdistributed feedback (DFB) lasers and distributed Bragg reflector (DBR)lasers. Each DFB or DBR laser in the laser array can be tuned and lockedin a channel, and modulated individually.

One of unsolved problems with DFB or DBR MWLs is uneven wavelengthdrifting that can cause cross talks. The output wavelength of a channeldepends upon the combined effects of junction temperature and injectioncurrents (diode pumping current, wavelength tuning current, and phaseshifting current). The channel tuning mechanisms of current MWL arraysare very complex. Since the output wavelength of an individual laser inthe array is a function of its junction temperature, any fluctuation inthe temperature of the diode will cause its output wavelength to drift.To keep output wavelengths locked in their channels, it is essential tomaintain the junction temperature constant. Heat sinks capable ofprecisely controlling temperature are ordinarily used to keep outputwavelengths stable. Also, the costs for making such laser arrays arevery high.

In shared-gain MWLs, laser channels share one gain region by integratingmulti-resonance feedback elements with one gain media, thereby yieldinga number of output wavelengths. One of the advantages of this design isstable output wavelength spacing even when all output wavelengths driftsimultaneously. It is more difficult to modulate individual channels formost of the existing shared-gain MWLs than for MWL arrays. U.S. Pat. No.6,289,032 discloses a self-collimating MWL laser, which simultaneouslypermits broad-beam collimation and monomode operation, with simultaneousemission of multiple wavelengths from a single aperture. While thisdesign results in stable wavelength spacing, it does not allow direct orinternal modulation of each individual wavelength. This design may havea limited channel capability.

DISCLOSURE OF THE INVENTION

The objective of this invention is to provide a multi-groupmulti-wavelengths laser source for optical networks especially for DWDMoptical fiber communication systems. The laser system disclosed in thisinvention has several advantages over conventional DFB and DBR lasers.In one aspect, it has a large channel capacity. In anther aspect, it isthermally and electrically stable in output wavelengths and channelspacing. In addition, the laser system can have a selectable bandwidthas broad as the full gain spectrum of the active medium. Finally, it iscost-effective in production.

The basic elements of the invented laser system include a group ofactive waveguides arranged in a matrix form for providing optical gain,a wavelength selectable optical device that is able to selectively feedback lights with different wavelengths, and an optical pumping mechanismor module for causing electron-population inversion in the activewaveguides. The active waveguides used in the exemplary embodimentsinclude optically active fibers and glass-based or crystal-based activewaveguides. A fiber can be made optically active by doping it with rareearth elements such as erbium and erbium/ytterbium (Er/Yb).

In one of the embodiments, the active waveguides are erbium-dopedfibers. FIG. 1 shows the energy diagram of the three-level energy systemof erbium ion (Er³⁺). The erbium-doped fiber pumped by 0.98 μm or 1.48μm light can amplify 1.55 μm optical signal. As shown in the diagram,light at the wavelength of 0.98 μm is absorbed by the erbium ions; andthe absorbed photons excite the erbium ions and cause them to transitfrom ground state to higher energy level, ⁴I_(11/2). The excited erbiumions then rapidly decay non-radiactively to a long-lived metastablestate, ⁴I_(13/2). The population of erbium ions in metastable state,⁴I_(13/2), is accumulated. The population of erbium ions in metastablestate may also be directly produced by pumping the erbium ions withlight at 1.48 μm. The transition of an erbium ion from the metastablestate to the ground state is a radiactive process that emits a photon atthe wavelength around 1.55 μm. This process may occur spontaneously, butit is much more probable when it is stimulated by a traveling photonaround 1.55 μm. This stimulated emission provides an optical gain of thelight around 1.55 μm as it travels through the erbium-doped fiber.

An optical cavity is formed in a piece of erbium-doped fiber by makingthe facets at both ends highly reflective. This can be done bytraditional methods such as thin-film coating and distributed Bragggrating. If the gain of light in a round trip in the optical cavity isbigger than optical loss, a fiber laser is formed. Since the techniqueof fabricating erbium/ytterbium (Er/Yb) doped fibers is well developed,they are used in the embodiment.

In contrast to the shared-gain MWL designs, this invention uses awavelength selectable optical device (FIG. 2 b) as a shared feedbackmirror for multiple gain regions. The wavelength selectable opticaldevice 10 contains a substrate layer 11, a grating layer 14, and awaveguide layer 13, which is non-uniform in its thickness or refractiveindex. When the optical device 10 is used as a feedback mirror at one ofthe end facets of an optically active fiber bundle (FIG. 5), it can feedlights with different wavelengths back to different optically activefibers. The optical device can also function as output couplers forgenerating multi-group wavelength outputs.

The principle upon which the wavelength selectable optical device worksas a wavelength selectable feedback mirror is guided mode resonance.Guided mode resonance occurs in waveguide gratings where guided modesthat would be supported by the waveguide without refractive indexmodulation are possible. However, since there is a periodic modulationor perturbance of the refractive index in or around the waveguide layer,the propagation constant β_(i) (See following Equation 2) becomes acomplex number and the imaginary part of β_(i) cannot be neglected.Thus, the waveguide modes cannot propagate without loss in thewaveguide. This structure is called a “leaky” structure because theenergy from the guided-mode does not propagate within the waveguide butleaks out of the structure. In this “leaky” structure, the energy of theincident optical wave is “fed” by the diffractive element into theperiodically modulated or perturbed waveguide, then the “leaky” mode iscoupled into certain space-harmonic waves, which are propagating waves.However, due to the phase-matching conditions, the “feeding” is stronglyselective with respect to the incident wavelength, the angle ofincidence, and the polarization state of the incident wave. Only theenergy from the incident wave that strictly satisfies the resonanceconditions can be fed into the structure. For the visible and nearinfrared range, the grating period Λ is in most cases in the sub-micronscale to allow only zero diffraction orders to propagate in reflectionand transmission while all higher order waves are cut off. In this case,100% reflection can be obtained at a desired narrow wavelength range.The bandwidth is typically less than a few nanometers while side bandshave low reflectivity. Thus, the optical device can be used as awavelength selectable mirror.

The guided-mode resonance phenomenon is well described by the rigorouscoupled-wave theory (S. S. Wang, R. Magnusson, J. S. Bagby, and M. G.Moharam, “Guided-mode resonances in planar dielectric-layer diffractiongratings,” J. Opt. Soc. Am. A, Vol. 8, pp. 1470-1475, August 1990; S. S.Wang and R. Magnusson, “Multilayer waveguide-grating filters,” Appl.Opt., Vol. 34, pp. 2414-2420, May 1995; and T. K. Gaylord and M. G.Moharam, “Analysis and applications of optical diffraction by gratings,”Proc. IEEE, Vol. 73, pp. 894-937, May 1985). The coupled-wave equationsgoverning wave propagation in the waveguide can be expressed as$\begin{matrix}{\frac{\mathbb{d}^{2}{{\hat{S}}_{i}(z)}}{\mathbb{d}z^{2}} + {\quad{{{{\left\lbrack {{k^{2}ɛ_{g}} - {k^{2}\left( {{\sqrt{ɛ_{g}}\sin\quad\theta} - {i\frac{\lambda}{\Lambda}}} \right)}^{2}} \right\rbrack{{\hat{S}}_{i}(z)}} + {\frac{1}{2}k^{2}{{\Delta ɛ}\left\lbrack {{{\hat{S}}_{i + 1}(z)} + {{\hat{S}}_{i - 1}(z)}} \right\rbrack}}} = 0},}}} & (1)\end{matrix}$where Ŝ_(i)(z) is the amplitude of the inhomogeneous plane wave of thei-th space harmonic, k=2π/λ is the free space wave number,Δε=(ε_(H)−ε_(L))/2 is the permittivity modulation, ε_(g)={overscore(ε_(g))}(X)=(ε_(H)+ε_(L))/2 is the average permittivity of the waveguidelayer, Λ is the grating period, and λ is the free-space wavelength. AsΔε→0 (weak modulation), allowingβ_(i) =k(ε_(g) ^(1/2) sin θ−iλ/Λ)  (2)equation (1) becomes $\begin{matrix}{{\frac{\mathbb{d}^{2}{{\hat{S}}_{i}(z)}}{\mathbb{d}z^{2}} + {\left( {{k^{2}ɛ_{g}} - \beta_{i}^{2}} \right){{\hat{S}}_{i}(z)}}} = 0.} & (3)\end{matrix}$

Equation (3) has the same appearance as the wave equation associatedwith an unmodulated slab waveguide. Similar to the eigenvalue of theunmodulated slab waveguide, the corresponding eigenvalue equation of themodulated waveguide is, in this limit, $\begin{matrix}{{\tan\left( {\kappa_{i}d} \right)} = \frac{\kappa_{i}\left( {\gamma_{i} + \delta_{i}} \right)}{\kappa_{i}^{2} - {\gamma_{i}\delta_{i}}}} & (4)\end{matrix}$for TE polarization, and is $\begin{matrix}{{\tan\left( {\kappa_{i}d} \right)} = \frac{ɛ_{g}{\kappa_{i}\left( {{ɛ_{3}\gamma_{i}} + {ɛ_{1}\delta_{i}}} \right)}}{{ɛ_{1}ɛ_{3}\kappa_{i}^{2}} - {ɛ_{g}^{2}\gamma_{i}\delta_{i}}}} & (5)\end{matrix}$for TM polarization, where κ_(i)={square root}{square root over(ε_(g)k²−β_(i) ²)}, γ_(i)={square root}{square root over (β_(i)²−ε₁k²)}, and δ_(i)={square root}{square root over (β² _(i)−ε₃k²)}.Equations (4) and (5) can be used to predict approximately thewavelength and incident angle location of the resonance for a givenstructure. The propagation constant, β_(i), of the waveguide grating inthe limit of Δε→0 is thus determined explicitly by the basic waveguidegrating parameters, grating period Λ, average permittivity of thewaveguide layer, ε_(g), the thickness of the waveguide layer, incidentangle, θ, the free space wavelength, λ, and mode index i.

The spectral response of a guided-mode resonant reflective filterpredicted by this theory is very close to the ones obtainedexperimentally (See “High-efficiency guided-mode resonance filter”, Z.S. Liu, S. Tibuleac, D. Shin, P. P. Young, and R. Magnusson, OpticsLetters, Vol. 23, No. 19, Oct. 1, 1998). The peak reflection wavelengthof a wavelength selectable optical device is determined by parameterssuch as grating periods, grating fill factors, refractive indices (thesquare of permibility) of the substrate, waveguide, and grating layers,input medium, and the thickness of the waveguide layer at the positionwhere the resonant modes occur. Any changes in these parameters willcause a shift in the wavelength of the peak reflection. Thus, when thoseparameters are non-uniform, the wavelength selectable optical device isable to reflect different wavelengths at different positions along thenon-uniform direction. The most convenient parameters for achievingvarious peak reflection wavelengths are the thickness of the waveguidelayer and the grating period of the grating. Making a waveguide layerwith non-uniform refractive indices is more complicated, but existingtechniques can be modified for this purpose. Equations (4) and (5) canalso be used to estimate the peak reflection wavelength for any point ona wavelength selectable optical device with multiple non-uniform deviceparameters.

FIG. 2 a illustrates a qualitative relationship between the peakreflection wavelengths of the optical device and the positions on theoptical device. FIG. 3 a shows theoretically predicted reflectionspectra for an optical device containing a waveguide layer ofnon-uniform thickness using the following device parameters: refractiveindex of substrate or spacer=1.47, refractive index of the waveguidelayer=2.0, refractive index of grating=1.5, refractive index of themedium above the surface-relief grating=1.0, thickness of grating=50 nm,grating period=920 nm, the separation distance between any two adjacentpoints=0.5 mm, thickness of the wavelength layer is from 317 nm to 371nm, corresponding to the position from 0 to 3.5 mm on the opticaldevice, as shown in FIG. 3 b. The incident lights and reflected lightsare TE (e.g., the electric vector normal to the grating vector)polarized. For convenience, only eight reflection spectra for eightevenly separated points on the optical device are computed. As shown inFIG. 3 a, all eight reflection peaks are evenly separated in thewavelength range from 1530 nm to 1565 nm. However, all wavelengths from1530 nm to 1565 nm are available as the peak reflection wavelengthswhile their individual output wavelength spacing for a specific opticaldevice may be constrained by the geometry of active waveguides withwhich the optical device is used. For a given number of activewaveguides in a defined geometrical arrangement in a laser matrix, anywavelength can be assigned, as the peak refection wavelength, to any ofthe active waveguides by designing the profile of non-uniformparameters.

Theoretical reflection spectra of an optical device with non-uniformgrating periods are shown in FIG. 4 a. The device parameters used in thecomputation are as follows: refractive index of substrate orspacer=1.47, refractive index of the waveguide layer=2.4, refractiveindex of grating=2.0, refractive index of the material embedding thegrating=1.5, thickness of the waveguide layer=350 nm, thickness ofgrating=50 nm, thickness of the embedding layer=300 nm (exclusive of thegrating thickness), and grating periods varied from 718.5 nm to 775.1 nm(FIG. 4 b). Peak reflection wavelengths can be anywhere from 1500 nm to1600 nm. By designing a proper non-uniform grating period profile for agiven active waveguides geometry, it is possible to achieve evenlyseparated reflection peaks or desirable wavelength spacing combs.

While the two computations are conducted for cases involving only onevarying device parameter, it is obvious to predict refection wavelengthsfor an optical device with more than one varying parameter in anydirection along the optical device.

The number of output wavelengths is determined by the number of activewaveguides and their layout in the matrix. The active waveguides areidentical to each other except they are located in different locationsso such that the lights from them are able to strike the different partof area on the optical device. Of course, the output wavelength range ofthe laser matrix must fall within the gain spectrum of the activewaveguides.

The output wavelength spacing between two adjacent lasers depends uponthe degree of the non-uniformity of relevant parameters of the opticaldevice and the distance between two adjacent active waveguides at apoint near the optical device. The wavelength spacing can be arbitrarilysmall because the difference in the parameters between two adjacentactive waveguides can be arbitrarily small.

All layers of the wavelength selectable optical device can be made ofdielectric materials such as SiO2, Si3N4, HfO2, Al2O3, and TiO2 orsemiconductor materials such as Si, InP, GaAs, AlGaAs, and InPGaAs. Toimprove the line shapes of its reflection spectra, the wavelengthselectable optical device may further include any or all of thefollowing three components: a thin-film layer on the top of the gradingsurface, a thin-film layer between the grating layer and the waveguidelayer, and a thin-film layer between the waveguide layer and thesubstrate.

The wavelength selectable optical device can be externally mounted tothe body containing an active waveguide matrix to form external opticalcavities. An optical device can be assembled with one of its surfacesfacing one of the light-emitting facets of the active waveguides, with amicro-lens matrix placed between the optical device and the activewaveguides.

The wavelength selectable optical device used in the present inventionis a passive element. No injection current flows through it. Thus, therefractive indices of all layers of materials of the device are stable.Since the output wavelengths depend only upon the positions on thedevice, the output wavelengths of the laser matrix will be stable evenwhen the powers of pumping lights are varied. Furthermore, the devicecan be fabricated using materials with high thermal stability, thus theoutput wavelengths of the laser matrix are thermally stable as well.

In summary, a multi-group multi-wavelength laser matrix is achieved byusing a wavelength selectable optical device as a shared feedback mirrorin one of the end facets of a laser matrix consisting of identicalactive waveguides. The laser system can provide multiple signal channelsfor multiple optical fibers. The outputs from the laser matrix featuresingle-mode, narrow-linewidths, highly polarized beams, arbitrarywavelength spacing, high thermal and electrical stability, and lowdivergence. Those features make this invented laser system a good lasersource for optical networks, especially for DWDM systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the energy level diagram of Er³⁺.

FIG. 2 a illustrates qualitative refection spectra of a wavelengthselectable optical device.

FIG. 2 b illustrates a schematic view of a wavelength selectable opticaldevice.

FIG. 3 a illustrates reflection spectra predicted for a wavelengthselectable optical device containing a waveguide layer of non-uniformthickness.

FIG. 3 b illustrates the thickness profile of the wavelength selectableoptical device used in FIG. 3 a computation.

FIG. 4 a illustrates reflection spectra predicted for a wavelengthselectable optical device containing a grating layer with non-uniformgrating periods in one direction.

FIG. 4 b illustrates the grating period profile of the wavelengthselectable optical device used in FIG. 4 a computation.

FIG. 5 illustrates a fiber laser matrix for generating multi-groupmulti-wavelengths.

FIG. 6 a illustrates the wavelength output map of a fiber laser matrixwhere the end facets are arranged in a square form.

FIG. 6 b illustrates the wavelength output map of a fiber laser matrixwhere the end facets are arranged in a triangle form.

FIG. 7 illustrates a diode-pumped crystal-based waveguide laser matrix.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one of the embodiments, active waveguides used in a laser matrix areerbium-doped optical fibers. The optical cavities of the fiber lasermatrix are formed by attaching one end of an erbium-doped fiber bundleto a wavelength selectable device and by coating the other end of thefiber bundle with a thin-film stack of high reflectivity. The thin-filmlayer has a reflection peak centered at 1.55 μm of wavelength.

The optical device has different peak reflection wavelengths atdifferent positions on the optical device, and each fiber laser has anoutput wavelength corresponding to the peak reflection wavelength of theoptical device at the corresponding position. When such a system ispumped by 0.98 μm or 1.48 μm pumping light, it can generate laseroutputs with multi-group multi-wavelengths. Each fiber laser in thelaser matrix can be designed to posses a single-mode, highly polarized,and narrow-linewidth output. Of course, all the output wavelengths arewithin the gain spectrum of the erbium-doped fibers.

The detailed structure of the fiber laser matrix is shown in FIG. 5. Thekey components include an erbium-doped fiber bundle 20, a highlyreflective thin-film coated facet 21 at one ends of the erbium-dopedfiber bundle, a wavelength selectable optical device 10, and anreceiving fiber bundle 30. The optical device 10 contains a spacer 11(equivalent to a substrate), a waveguide layer 13 with non-uniformthickness or refractive index, and a grating layer 14 on the top of thewaveguide layer 13. The refractive index of the spacer is less than thatof the waveguide layer. The erbium-doped fiber bundle 20 is arranged toform a matrix with the end facets of the fibers at one end (not shown)falling on a plane. The end facets of the fibers are further arranged toform a matrix, which collectively face or are attached to the opticaldevice 10. The end facets of the matrix may be arranged in the form ofsquare (FIG. 6 a) or in the form of triangle (FIG. 6 b). The end-facetmatrix of the receiving fiber bundle 30 have exactly the same layout asdoes the erbium-doped fiber bundle 20 although missing individualreceiving fibers will not adversely affect the performance of otherfiber lasers.

The wavelength output map for this specific embodiment is illustrated inFIGS. 6 a and 6 b. There is a 6 rows×8 columns end-facet matrix. Thedirection of the non-uniformity of the optical device is parallel withthe row direction of the end facets in the matrix (FIG. 6 a). Thus,there are 8 different wavelengths, corresponding to the 8 fibers in eachrow. The 6 fibers in each column in the end-facet matrix have the sameoutput wavelength since the local parameters in those positions on theoptical device are identical in this example. Thus, there are 6identical groups of output wavelengths, with each group having 8different output wavelengths. Generally, fiber-laser matrices cancontain N rows and M columns fibers. The system can generate N groups ofM wavelengths. When it is used in a fiber optical network, it canprovide laser sources of M channels to N trunk fibers. As a specialcase, when M is one, a fiber-laser array for generating multi-wavelengthoutputs is resulted.

The end-facet layout in the end-facet matrix can also be arranged withthe maximum fill factor (to occupy the least volume) as shown in FIG. 6b according to another example of the invention. Like the previousexample, the non-uniformity direction of the optical device is parallelto the row direction of end-facet matrix of the erbium-doped fiberbundle. The end-facet matrix in this example has 6 rows, each of whichcontains 8 erbium-doped fibers. Every alternative row is displaced alongthe non-uniformity direction by half of the distance between twoadjacent erbium-doped fibers. All rows are packed together so they areable to contact each other. As shown in the FIG. 6 b, the centers of anytwo adjacent end facets and the center of the nearest end facet of aneighbor row form a triangle. Every two adjacent rows of the laserfibers can generate a group of outputs with 16 different wavelengths. Intotal, the matrix has 3 identical groups outputs, with each group having16 output wavelengths. In general, when the end facets in a N by Mmatrix are arranged with the maximum fill factor, the laser matrix hasN/2 groups identical outputs, each of which have 2M different outputwavelengths. When it is used in a fiber optical network, it can providelaser sources of 2M channels to N/2 trunk fibers.

In the third example of the embodiments, the concept of this inventionis extended to diode-pumped crystal laser. Shown in FIG. 7 is amulti-group multi-wavelength diode-pumped crystal-laser matrix. The keycomponents are a plurality of glass- or crystal-based active waveguide42, a high-reflection thin-film coated facet 41 at one of the ends ofthe active waveguides 42, an optical device 10, and a number of pumpingdiode laser bars 43. The optical device has a similar structure as thosedescribed in the previous examples. Laser cavities are formed by thehigh-reflection coated facets 41, the active waveguides 42, and theoptical device 10. The active waveguides 42 in the waveguide matrixpumped by laser-diode-bar 43 provide optical gain. For the same reasondiscussed in the first sample of the fiber-laser matrix, the lasermatrix can generate laser outputs with N groups of M wavelengths.

A laser matrix using a wavelength selectable optical device may serve asa laser source for DWDM systems. The disclosed MWL matrix in thisinvention features compact size, high stability in wavelength andwavelength spacing, broad wavelength selectivity, convenience of use,and low costs for mass production. When a fixed manufacturing process isdeveloped for mass production, individual units are expected to achieveuniform performance characteristics. By designing the profile ofnon-uniform parameters for a wavelength selectable optical device, eachreflection wavelength for a corresponding laser unit can be locked intoa particular wavelength channel. For a wavelength selectable opticaldevice that is designed to have a linear relation between its peakreflection wavelength and its position in one direction, the outputwavelengths may be shifted by changing the position of the opticaldevice along the row direction of the laser matrix. This method may beuseful in some situations to correct errors in designing and fabricatingthe optical device.

The wavelength selectable optical device can be fabricated usingexisting techniques. Methods of fabricating grating on a surface are artknown by those skilled in the art. Typical techniques includeholographic interference, phase mask, electron beam writing, andlaser-beam writing. Electron beam writing and laser-beam writing can beused to fabricate grating with varying grating periods. Thin-filmdeposition, a well-known technique, can be used for fabrication of thewaveguide layer. Taped or stepped waveguide layer can be fabricated byusing thin-film deposition technique in combination with a preciselycontrolled moving mask on the deposited surface. Perhaps, selectiveetching process may be used to create non-uniform structures (U.S. Pat.No. 6,309,975 to Wu, et al.). Layers with non-uniform indices may bemade by thin-film deposition using two or more material sources. Othercomponents such as active waveguides and light-pumping modules arecommercially available.

In the exemplary embodiments of the invention, specific components,arrangements, and assemble processes are used to describe the invention.Obvious changes, modifications, and substitutions may be made by thoseskilled in the art to achieve the same objectives of this invention. Theexemplary embodiments are, of course, merely examples and are notintended to limit the scope of the invention. The present invention isintended to cover all other embodiments that are within the scope of theappended claims and their equivalents.

1. A laser system comprising: An optical device comprising: a substratelayer; a waveguide layer on the substrate layer; a grating layer on thewaveguide layer on the side opposite to the substrate layer; and meansfor varying reflection wavelengths along any direction of the waveguidelayer; At least three active waveguides having first end facets andsecond end facets, the first end facets of the active waveguides beingattached to the optical device with the first end facets being arrangedin the form of matrix, the second end facets being coated with athin-film stack, At least one light supply module which is capable ofgenerating pumping light with its energy sufficiently high for excitingthe active waveguides; the thin-film stack on the second facets beingsubstantially transparent to the pumping light but is opticallyreflective to the light for output; Means for coupling laser lights fromthe laser system for output.
 2. The laser system of claim 1 wherein themeans for varying reflection wavelengths is selected from a groupconsisting of non-uniform thickness of the waveguide layer along anydirection on its central plane, non-uniform refractive index of thewaveguide layer along any direction on its central plane, non-uniformgrating periods in the grating layer along any direction on the layer,and combinations thereof.
 3. The laser system of claim 2 wherein theactive waveguides are optical fibers doped with a material selected froma group consisting of erbium and erbium/ytterbium, the light supplymodules are able to generate the pumping lights in wavelength selectedfrom a group consisting of 0.98 um, 1.48 um and combinations thereof,the thin-film stack on the second facets is transparent to the pumpinglights while it has high reflectivity to the light at the wavelengtharound 1.55 um.
 4. The laser system of claim 3 wherein the first endfacets of the active fibers are arranged in the form of matrix, with itsbasic elements substantially in the form of square shape.
 5. The lasersystem of claim 4 further comprising at least one receiving fiberattached to the optical device on the side opposite to the side to whichthe active fibers are attached, at least one of the receiving fibersbeing arranged with its axis falling in the extension lines of theactive fibers whereby the receiving fiber is able to receive laser beamsduring laser operation.
 6. The laser system of claim 5 wherein aplurality of the light supply modules provide the pumping lights ofdifferent intensities to the active fibers.
 7. The laser system of claim6 further comprising at least one component selected from a groupconsisting of a thin-film layer on the top of the grading surface, athin-film layer between the grating layer and the waveguide layer, and athin-film layer between the substrate and the waveguide layer, andcombination thereof.
 8. The laser system of claim 5 wherein one lightsupply module provides the pumping light to the active fibers.
 9. Thelaser system of claim 5 wherein the number of a plurality of thereceiving fibers is equal to the number of the active fibers, and theaxes of the receiving fibers fall in the extension lines of the activefibers.
 10. The laser system of claim 4 further comprising a micro-lensmatrix between the optical device and the active fibers.
 11. The lasersystem of claim 3 wherein the first end facets of the active fibers arearranged to form a matrix, with its basic elements substantially in theform of triangle shape.
 12. The laser system of claim 11 furthercomprising at least one receiving fiber attached to the optical deviceon the side opposite to the site to which the active fibers areattached, at least one of the receiving fibers being arranged with itsaxis falling in the extension lines of the active fibers whereby thereceiving fiber is able to receive laser beams during laser operation.13. The laser system of claim 12 wherein a plurality of the light supplymodules provide the pumping lights of different intensities to theactive fibers.
 14. The laser system of claim 13 further comprising atleast one component selected from a group consisting of a thin-filmlayer on the top of the grading surface, a thin-film layer between thegrating layer and the waveguide layer, and a thin-film layer between thesubstrate and the waveguide layer, and combination thereof.
 15. Thelaser system of claim 12 wherein one light supply module provides thepumping light to the active fibers.
 16. The laser system of claim 12wherein the number of a plurality of the receiving fibers is equal tothe number of the active fibers, and the axes of the receiving fibersfall in the extension lines of the active fibers.
 17. The laser systemof claim 16 further comprising at least one component selected from agroup consisting of a thin-film layer on the top of the grading surface,a thin-film layer between the grating layer and the waveguide layer, anda thin-film layer between the substrate and the waveguide layer, andcombination thereof.
 18. The laser system of claim 3 further comprisinga micro-lens matrix between the optical device and the active fibers.19. The laser system of claim 3 wherein one light supply module providesthe pumping light to the active fibers.
 20. The laser system of claim 3wherein a plurality of the light supply modules provide the pumpinglights of different intensities to the active fibers.
 21. The lasersystem of claim 2 further comprising a micro-lens matrix between theoptical device and the active waveguides.
 22. The laser system of claim2 wherein one light supply module provides the pumping light to theactive waveguides.
 23. The laser system of claim 2 wherein a pluralityof the light supply modules provide the pumping lights of differentintensities to the active waveguides.
 24. The laser system of claim 1further comprising a micro-lens matrix between the optical device andthe active waveguides.
 25. The laser system of claim 1 wherein one lightsupply module provides the pumping light to the active waveguides. 26.The laser system of claim 1 wherein a plurality of the light supplymodules provide the pumping lights of different intensities to theactive waveguides.
 27. The laser system of claim 1 wherein the means forvarying reflection wavelengths is selected from a group consisting ofnon-uniform thickness of the waveguide layer along a first direction,non-uniform refractive index of the waveguide layer along the firstdirection, non-uniform grating periods in the grating layer along thefirst direction, and combinations thereof.
 28. The laser system of claim27 wherein the active waveguides are optical fibers doped with amaterial selected from a group consisting of erbium anderbium/Ytterbium, the light supply modules are able to generate thepumping lights in wavelength selected from a group consisting of 0.98um, 1.48 um and combinations thereof, and the thin-film stack on thesecond end facets is transparent to the pumping lights while it has highreflectivity to the light at the wavelength around 1.55 um.
 29. Thelaser system of claim 28 wherein the first end facets of the activefibers are arranged to form a matrix, with its basic elementssubstantially in the form of square shape.
 30. The laser system of claim29 further comprising at least one receiving fiber attached to theoptical device on the side opposite to the side to which the activefibers are attached, at least one of the receiving fibers arranged withits axis falling in the extension lines of the active fibers whereby thereceiving fiber is able to receive laser beams during laser operation.31. The laser system of claim 30 wherein a plurality of the light supplymodules provide the pumping lights of different intensities to theactive fibers.
 32. The laser system of claim 31 further comprising atleast one component selected from a group consisting of a thin-filmlayer on the top of the grading surface, a thin-film layer between thegrating layer and the waveguide layer, and a thin-film layer between thesubstrate and the waveguide layer, and combination thereof.
 33. Thelaser system of claim 30 wherein one light supply module provides thepumping light to the active fibers.
 34. The laser system of claim 30wherein the number of a plurality of the receiving fibers is equal tothe number of the active fibers, and the axes of the receiving fibersfall in the extension lines of the active fibers.
 35. The laser systemof claim 28 further comprising a micro-lens matrix between the opticaldevice and the active fibers.
 36. The laser system of claim 28 whereinthe first end facets of the active fibers are arranged to form a matrix,with its basic elements substantially in the form of triangle shape. 37.The laser system of claim 36 further comprising at least one receivingfiber attached to the optical device on the side opposite to the site towhich the active fibers are attached, at least one of the receivingfibers being arranged with its axis falling in the extension lines ofthe active fibers whereby the receiving fiber is able to receive laserbeams during laser operation.
 38. The laser system of claim 37 wherein aplurality of the light supply modules provide the pumping lights ofdifferent intensities to the active fibers.
 39. The laser system ofclaim 38 further comprising at least one component selected from a groupconsisting of a thin-film layer on the top of the grading surface, athin-film layer between the grating layer and the waveguide layer, and athin-film layer between the substrate and the waveguide layer, andcombination thereof.
 40. The laser system of claim 37 wherein one lightsupply module provides the pumping light to the active fibers.
 41. Thelaser system of claim 37 wherein the number of a plurality of thereceiving fibers is equal to the number of the active fibers, and theaxes of the receiving fibers fall in the extension lines of the activefibers.
 42. A laser system comprising: a body having a first surface onone side of the body and a second surface on the opposite side of thebody; at least three active waveguides arranged in the form of an matrixin the body; each of the active waveguide having a first end facetfailing in the first surface of the body and a second end facet fallingin the second surface of the body, the wave propagating direction ofeach of the activeguides being perpendicular to the second surface ofthe body, the second surface of the body being coated with ahigh-reflection thin-film stack; An optical device comprising: asubstrate layer; a waveguide layer on the substrate layer; a gratinglayer on the waveguide layer on the waveguide layer on the side oppositeto the substrate layer; and means for varying reflection wavelengthsalong any direction of the waveguide layer, the optical device beingsubstantially parallel with the second surface of the body whereby theresonant lights from the active waveguides are able to strike differentparts of the areas of the optical device during laser operation; and Atleast one pumping diode laser bar installed along the body for excitingthe active waveguides; and means for coupling laser beams from the lasersystem for outputs.
 43. The laser system of claim 42 wherein the meansfor varying reflection wavelengths is selected from a group consistingof non-uniform thickness of the waveguide layer along a first direction,non-uniform refractive index of the waveguide layer along the firstdirection, non-uniform grating periods in the grating layer along thefirst direction, and combinations thereof.
 44. The laser system of claim43 wherein the first end facets of a plurality of the active waveguidesare arranged in the form of matrix.
 45. The laser system of claim 44further comprising at least of one component selected from a groupconsisting of a thin-film layer on the top of the grading surface, and athin-film layer between the grating layer and the waveguide layer, and athin-film layer between the substrate and the waveguide layer, andcombinations thereof.
 46. The laser system of claim 45 wherein the diodelaser bars are able to provide pumping lights to the active waveguidesat various pumping levels during laser operation.
 47. The laser systemof claim 46 further comprising a micro-lens matrix between the opticaldevice and the first surface of the body.
 48. The laser system of claim45 further comprising a micro-lens matrix between the optical device andthe first surface of the body.
 49. The laser system of claim 44 whereinthe diode laser bars are able to provide pumping lights to the activewaveguides at various pumping levels during laser operation.
 50. Thelaser system of claim 49 further comprising a micro-lens matrix betweenthe optical device and the first surface of the body.
 51. The lasersystem of claim 43 wherein the diode laser bars are able to providepumping lights to the active waveguides at various pumping levels duringlaser operation.
 52. The laser system of claim 51 further comprising amicro-lens matrix between the optical device and the first surface ofthe body.